When you add more columns to a running installation, you must re-index all content in order to re-partition the index columns. A complete re-build of a multi-column index may take several days.

You can scale up by indexing more items per column. The default indexer configuration for each column has five partitions, each with a maximum of 6 million items. In order to keep index freshness high, the two first partitions should preferably have very little content. Effectively, the default configuration is suitable for up to 15 million items, with the three large partitions holding close to the maximum of 6M items each. Exceeding 15 million items will make indexing progressively slower until you meet the default configuration’s absolute limit of 30 million items. You can tune the column capacity up to 40 million items per column by increasing the number of partitions to ten. This will yield eight large partitions with 6 million items each. You may want to do this tuning, and save hardware cost, for scenarios with few content updates and moderate query volume or in case the size of the searchable content is very small. An example of the latter may be PowerPoint presentations with lots of graphics. They may be large in source volume size but contain very little searchable content. For more information about index capacity tuning, refer to Performance and capacity tuning (FAST Search Server 2010 for SharePoint).